Recently, hermetic motor compressors (hereinafter referred to simply as compressors) with reduced vibration and reduced noise emission are demanded. Because conventional refrigerants have a tendency to cause ozone layer damage or global warming, the use of hydrocarbon refrigerants having an ozone damaging coefficient of zero and a global warming coefficient of zero is commenced to protect global environment.
FIG. 6 depicts a conventional compressor as disclosed in Japanese Patent Publication (examined) No. 1-47632, which includes a hermetically sealed casing 1 and an integrated structure 4 accommodated in the casing 1. The integrated structure 4 is made up of a compression section 2 and a drive section 3 integrally formed with each other. The compression section 2 includes a cylinder 5, a piston 6 reciprocally mounted in the cylinder 5, a crankshaft 7 connected to a rotor 3a of the drive section 3 for rotation together therewith, and a connecting rod 8 for connecting the piston 6 to the crankshaft 7 to convert rotation of the crankshaft to a reciprocating motion of the piston 6.
The casing 1 has a generally flat bottom wall 1a and a generally cylindrical side wall1b unitarily formed with each other. A gas inlet tube 10 is welded to the side wall 1b, while a plurality of legs 11 are welded or secured to the bottom wall 1a. The integrated structure 4 is supported by a stay 12 welded to the inner surface of the side wall 1b, while the drive section 3 is electrically connected to a power source (not shown) via a hermetic terminal 13 hermetically welded to the side wall 1b.
In the above-described construction, because the bottom wall 1a is generally flat, the plurality of legs 11 can be welded thereto with good workability. Also, because the side wall1b is generally cylindrical and not spherical, the stay 12 can be welded thereto with good workability.
The casing 1 is, however, low in rigidity due to the generally flat shape of the bottom wall 1a and the generally cylindrical shape of the side wall 1b. Because of this, the casing 1 oscillates slightly and generates noise, or sound produced during operation of the integrated structure 4 accommodated therein leaks through the generally flat or cylindrical portion, thus increasing the noise.
Particularly, in applications where a hydrocarbon refrigerant such as, for example, isobutane is used for a compression refrigerant, the concentration of circulating refrigerant is reduced during cyclic operation of the compressor at the same condensation and evaporation temperatures as in the operation with the use of a conventional refrigerant (for example, CFCR12, HFCR134a or the like) including fluorine or chlorine. Accordingly, enlargement of the internal volume of the cylinder 5 is required, which in turn causes an increase in unbalanced mass, thus increasing vibration and generating noise.
The present invention has been developed to overcome the above-described disadvantages.
It is accordingly an objective of the present invention to provide a hermetic motor compressor capable of reducing vibration and noise emission even if the unbalanced mass is increased which has been hitherto caused by enlargement of the internal volume of the cylinder.